Field
The present invention relates to a method of making a root end joint of a wind turbine blade and a root segment for such a joint.
Description of the Related Art
Most modern day wind turbine blades are manufactured with either carbon or glass fiber reinforced plastic. As is well known in the art, at the root (hub) end of the blade, this is typically glass fiber combined with epoxy resin (and sometimes polyester, vinylester and polyurethane resin families). The typical manufacturing methods are vacuum resin infused or pre-preg methods.
The thickness of the laminate required at the root end can be very high when compared to some other parts of the wind turbine blade and is often in the range of 50 mm-80 mm thick but with more modern blades can be up to 150 mm thick. This high thickness can cause manufacturing problems. When the resin system is curing, it generates heat in an exothermic reaction. In the thick areas of the root, the heat generated can become so much that it causes damage with the finished component such that it cannot be used.
A typical method of forming the root end is shown in FIGS. 1A-1C. In this, the matrix of dry fabric is laid up in the mould of a suitable shape. The resin is then infused and cured to the finished part as shown in FIG. 1B).
Once the root component of the blade is cured, it is then typically transferred to a drilling location where a number of holes 4 are drilled in the end of the root laminate to allow metal root inserts with female screw threads to be bonded or mechanically fixed in place. Two semi-circular sub-assemblies are then joined together to make the finished root end joint as shown in FIG. 1c) US 2009/0226320, WO 2010/092168 and EP 2 341 240 all show similar arrangements where the roots are further broken down into quarter circle segments. Drilling of the holes is a time-consuming and expensive process and the amount of heat generated by the drilling must be carefully controlled so as not to damage the material. As the accuracy of drilling is very important, large jigs are required. Once the hole is drilled, the metallic insert is then bonded or mechanically held into position in the hole. The attachment of the root insert is very critical as these are very high load components and can be prone to failure.
FR 2 863 321 discloses a number of root segments which are imbedded within the end face of a wind turbine and each have a plurality of threaded inserts by virtue of which the blade is connected to the hub. A similar disclosure is contained in EP 2 400 147 published after the priority date of the present application.